Process for producing nitriles



United States Patent 3,225,080 PROCESS FOR PRODUCING NITRILES Kunio Nakagawa, Nishinomiya-shi, Hyogo, and Teruji Tsuji, Suita-shi, Osaka, Japan, assignors to Shionogi & Co., Ltd., Osaka, Japan No Drawing. Filed Oct. 2, 1962, Ser. No. 227,723 Claims priority, application Japan, Oct. 3, 1961, 36/35,934' 5 Claims. (Cl. 260-465) The present invention relates to a process for oxidizing an organic compound, and particularly to a process for oxidizing an amine to the corresponding nitrile. More particularly, it relates to the use of nickel peroxide for the oxidation of the amine having a structure represented by the formula: CH NH in the molecule to the corresponding nitrile having a structure represented by the formula: CN in the molecule.

In the present specification, the term nickel peroxide is expediently applied to designate the black, hydrous, higher oxides of nickel which are formed by reaction between a strong oxidizing agent, such as alkali hypohalites or alkali persulfates, and freshly precipitated nickelous hydroxide.

With respect to the method for oxidizing amines to nitriles, there have been heretofore known the process for oxidizing amines in vapor phase using silver as a catalyst [Peters et al., Ind Eng. Chem., 40, 2046 (1948)], and the process for oxidizing the same with bromine and sodium hydroxide [Hotfmam Ber., 17, 1884 (1920)]. In either case, however, the yield of nitriles is very low. There has been also known that potassium permanganate or manganese dioxide can oxidize amines. However, the oxidation reaction proceeds up to aldehydes by the use of potassium permanganate [Goldschmitt, Ann, 435, 271 (1923) or it is interrupted at the stage of imines by the use of manganese dioxide [Highet et al., J. Am. Chem. Soc., 77, 4399 (1955)].

It has now been discovered that the oxidation of amines by nickel peroxide gives nitriles in a good yield. Thus, the amine having a structure represented by the formula: CH NH in the molecule is readily oxidized with nickel peroxide in a suitable medium to give the corresponding nitrile in a good yield.

With respect to the use of nickel peroxide as an oxidizing agent in the field of organic chemistry, there has been heretofore known only one literature, i.e. German Patent 127,388, in which toluene was oxidized with nickel peroxide to give benzaldehyde as a main product and benzoic acid as a by-product. However, no literature has disclosed the conversion of amines with nickel peroxide into nitriles.

Accordingly, a primary object of the present invention is to embody a process for oxidizing an amine to the corresponding nitrile. Another object of the invention is to embody a utilization method of nickel peroxide as an oxidizing agent suitable for the conversion of amines into nitriles. These and other objects will be apparent to those skilled in the art to which the present invention pertains from the subsequent description.

The process of the present invention comprises treating the amine having a structure represented by the formula: -CH NH in the molecule with nickel peroxide in a hydrous or anhydrous medium to give the corresponding nitrile having a structure represented by the formula: -CN in the molecule.

The starting amine may be employed in the free state or in the form of salt. However, when the salt is em- 3,225,080 Patented Dec. 21, 1965 ICC ployed, it is preferred to change the salt to the free state by the addition of an equivalent or slightly excess amount of a basic substance in advance of the oxidation reaction.

The nickel peroxide possessing a high oxidizing activity may be prepared by treating a nickel salt (e.g. nickel chloride, nickel sulfate, nickel carbonate, nickel nitrate) with a strong oxidizing agent such as alkali hypohalites (e.g. sodium hypochlorite, potassium hypochlorite, sodium hypobromite) or alkali persulfates (e.g. sodium persulfate, potassium persulfate) in an aqueous alkaline medium. One of the presently-preferred procedures for obtaining the highly active nickel peroxide is set forth as follows:

To a solution of nickel sulfate hydrate (NiSO,-6H O) (130 g.) in water (300 ml.), there is added dropwise a solution of sodium hydroxide (42 g.) in 6% sodium hypochlorite (300 m1.) while stirring, and the resultant mixture is stirred for about 30 minutes at a temperature between 10 and 25 C. The black precipitate is collected by filtration, washed with water to remove active chlorine and, after crushing the cake to powder, dried over anhydrous calcium chloride under reduced pressure.

The nickel peroxide is a black fine powder containing several amounts of water. The results of the quantitative analysis make it possible to give the molecular formula: Ni O -3H O or Ni(OH) to the oxidant, but the structure has not yet been confirmed. The nickel peroxide possesses usually about 0.30.4 10 g.-atom of available oxygen per gram (measured by titrating the iodine, produced from the reaction between the nickel peroxide and potassium iodide in acetic acid, with sodium thiosulfate), of which a considerable portion is lost gradually when heated, but remains for a long time when stored at room temperature under protection against atmospheric moisture. Since it has remarkably broad surface compared with its weight, the available oxygen can be used elfectively in the oxidation reaction. Owing to this character of the reagent, the present oxidation. can advantageously be completed in a short time normally with one to two equivalent amounts of the oxidant.

The optimum reaction conditions such as reaction medium, reaction temperature, reaction time and amount of the oxidant are more or less associated with the kind of the starting amines. Therefore, the preferable conditions may be decided on each case. As the reaction medium, there may be exampled water, a neutral inert organic solvent (e.g. benzene, toluene, ether, tetrahydrofuran, petroleum ether) and a mixture thereof. Although the reaction is ordinarily carried out from 30 to C., the higher or lower temperature is also operative, provided that the amount of the oxidant is proper. Especially, it may be noted as a characteristic of the present process that the reaction can proceed satisfactorily even at a lower temperature than 30 C. This may be greatly advantageous, when the present process is applied to the oxidation of unstable compounds for heat. The reaction time may be from 30 minutes to 6 hours, normally from 1 to 3 hours. The oxidant is employed usually from 1 .to 1.7 times the theoretical amount. As the large excess of the oxidant rather results in the poor yield of the product, .the amount is desired to be at the most two times the theoretical amount.

For the recovery of the reaction product from the reaction mixture, there may be adopted per se conventional separation procedures such as extraction, concentration, evaporation, filtration, distillation, recrystallization and chromatography. In this respect, the present process has an advantage that the oxidant can be readily separated from the reaction mixture by a simple operation, e.g. filtration. Alternatively, the reaction mixture may be shaken with a suitable water-immiscible organic added nickel peroxide 1.5 times the theoretical amount), and the resulting mixture is stirred for 1.5 hours at 60 C. The reaction mixture is shaken with ether. The ether extract is evaporated and the residue is crystallized from solvent whereby only the reaction product is retained in hexane to give 4-methoxybenz-onitrile (2.8 g.) melting at the organic solvent layer. 58 to 59 C.

The nickel peroxide employed in the oxidation reaction Example 4 can be i t g by s if profedure 2g. g To a solution of n-hexylamine hydrochloride (5.0 g.) treatmentho t il f? e 1 5 f 2 ng and sodium hydroxide (17.4 g.) in water (100 ml.), there agent Sue l a 1 y a Li or 3 g l a es is added nickel peroxide (30.6 g.), and the resultant mixaqueous a kahnelme g f e f ture is heated for 1.5 hours at 60 C. After cooling, Preferred g P g ures .2 g YE t the reaction mixture is filtered, extracted with ether, and ecte me peroxl 6 6 W1 evaporated. Distillation of the residue yields capronitrile st1rred with 6% sodium hypochlorite (about ten times (2 33 g) the quantity of nickel peroxide) in an aqueous alkaline 15 Example 5 medium for minutes, filtered, Washed with water and dried, To a solution of hex-amethylenediamine (5.0 g.) in As disclosed above, the nickel peroxide is usually once benzene theft? 1S adfiled nlckel PeTOXlde separated from the reaction mixture of a nickel salt and 5-) and t reunankmlxture 1S refluxed for hoursa strong oxidizing agent in an aqueous alkaline medium, 20 The reaction mixture is filtered and the filtrate 1S shaken and then subjected to the use as an oxidizing agent. with dilute sulfuric acid. The benzene layer is evaporated However, the nickel peroxide may be employed without and the neutral oily residue g.) is distilledunder rethe separation from the reaction mixture. For instance, duced Pressure give adlpoflltrllc bolllng at 126 when the reaction mixture of a nickel salt and an alkali t0 3 hypohalite in an aqueous alkaline medium is employed Example 6 1n the oxidation reaction as it is, the nickel per-ox1de 1n the mixture works as an oxidizing agent and changes to To a mlxtllre of 4'chl,orobenzylamlne hrdrochlonde nickelous hydroxide, which is spontaneously renewed to (3-56 sodlum hydroxlde and mckel sulfate nickel peroxide by the existing alkali hypohalite. Accord- 5- Water f f 13% 5021mm ingly, the amount f the oxidant to be empbyed may b 30 hypochlorite (30 g.) dropwise with stirring at 60 C., much decreased and the resultant mixture is heated for 40 minutes at The following examples set forth illustratively presenth Same temperature- The reacflon mlxture 1s extracted ly-preferred embodiments of the present invention. In f ether and evaporated to crude 4'chlorobenzo the examples, the abbreviations have the following sigmmle nificances: g., gram(s); ml., millilitre(s); and C., de- 35 Example 7 grees centigrade. Other abbreviations have conventional In the similar manner as shown in the above examples, significances. there are obtained the following results:

Nickel Reaction Reaction Reaction Yield Starting amine peroxide a solvent temperatime Produced nitrile (percent) ture 0.) (hour) 2-methylbenzylamine 1.5 1.5 2-methylbenzonitrile. 76.8 3-methylbenzyla-miue 1.5 60 1.5 3-methylbenzonitrile 78.7 4-methylbenzylamine 1.5 60 1.5 4-methy1benzonitrilc 75.2 z-nitrobenzylainine 1.5 60 1.5 2-nitrobenzonitrile 87.0 4-nitrobenzylamine 1.5 60 1.5 4-nitrobenzonitrile 55.5 2-chlorobenzy1amine. 1.5 60 1.5 2-chlorobenzonitrile 86.7 3-chlorobenzylarnine 1.5 60 1.5 3-chlor0benzonitrile 69.5 Furiurylarnine 1.1 5 0.5 2-furonitrile 62.5 Hexylamine 1.5 80 1.5 Capronitrile 72.7 Octylamine 1.5 80 1.5 Caprylonitrile. 95.8 Dodecylamine 1.5 80 1.5 Lauronitrile 80.7 Naphthalene-l-methylaminc 1.5 60 1.5 l-naphthonitrile 90.5

* Ratio of nickel peroxide to amine based on the available oxygen.

Example 1 Example 2 A mixture of benzylamine (4.28 g.) and nickel peroxide (34.6 g.) in benzene (100 ml.) is refluxed for 1.5 hours while stirring. Then, the reaction mixture is filtered to separate the oxidant and the filtrate is dried and evaporated to give the residue, which is distilled to give bonzonitrile (3.08 g.) boiling at 185 to 191 C.

Example 3 To a solution of 4-methoxybenzylamine hydrochloride (4.2 g.) in water (150 ml.), there is added sodium hydroxide whereby 4-methoxybenzylamine is obtained in the form of free base. To the resultant solution, there is The process of the present invention is generally applicable to the production of a nitrile from the corresponding primary alkyl and aryl amines. For instance, it can be adopted for the oxidation of methallylamine to methacrylonitrile, the latter being useful as a starting material in the production of synthetic rubbers and synthetic resins.

What is claimed is:

1. A process for oxidizing an amine selected from the group consisting of hexylamine, octylamine, dodecylamine, benzylamine, methylbenzylamine, methoxybenzylamine, chlorobenzylamine and nitrobenzylamine in the presence of nickel peroxide and in the liquid phase at a temperature between 30 and C., thereby producing the corresponding nitrile.

2. In a process for oxidizing primary amine with an oxidizing agent to the corresponding nitrile, the improvement wherein the reaction takes place in the liquid phase at a temperature between 30 and 90 C. and the oxidizing agent is nickel peroxide.

3. In a process for oxidizing alkyl primary amine with an oxidizing agent to the corresponding nitrile, the im- 3,225,080 5 6 provement wherein the reaction takes place in the liquid References Cited by the Examiner phase at a. temperature between 30 and 90 C. and the FOREIGN PATENTS oxidizing agent is nickel peroxide.

4. Process for preparing adiponitrile which comprises 1271388 8/1900 Germanyoxidizing hexamethylenediamine with nickel peroxide in 5 EN E the liquid phase at a temperature between 30 and 90 C. OTHE R REFER S 5. Process for preparing 1-naphthonitrile hi h Industrial and Engineering Chemistry, 1948, volume prises oxidizing naphthalene-l-methylamine with nickel Pages 2046-2053- peroxide in the liquid phase at a temperature between 30 nd 90 C, 10 CHARLES B. PARKER, Primary Examiner. 

1. A PROCESS FOR OXIDIZING AN AMINE SELECTED FROM THE GROUP CONSISTING OF HEXYLAMINE, OCTYLAMINE, DODECYLAMINE, BENZYLAMINE, METHYLBENZYLAMINE, METHOXYBENZYLAMINE, CHLOROBENZYLAMINE AND NITROBENZYLAMINE IN THE PRESENCE OF NICKEL PEROXIDE AND IN THE LIQUID PHASE AT A TEMPERATURE BETWEEN 30* AND 90* C., THEREBY PRODUCING THE CORRESPONDING NITRILE. 